Sustainable intensification calls for agroecological and adaptive management of the agrifood system. Here, we focus on intercropping and how this agroecological practice can be used to increase the sustainability of crop production. Strip, mixed, and relay intercropping can be used to increase crop yields through resource partitioning and facilitation. In addition to achieving greater productivity, diversifying cropping systems through the use of strategic intercrops can increase yield stability, reduce pests, and improve soil health. Several intercropping systems are already implemented in industrialized agricultural landscapes, including mixed intercropping with perennial grasses and legumes as forage and relay intercropping with winter wheat and red clover. Because intercropping can provide numerous benefits, researchers should be clear about their objectives and use appropriate methods so as to not draw spurious conclusions when studying intercrops. In order to advance the practice, experiments that test the effects of intercropping should use standardized methodology, and researchers should report a set of common criteria to facilitate cross-study comparisons. Intercropping with two or more crops appears to be less common with annuals than perennials, which is likely due to differences in the mechanisms responsible for complementarity. One area where intercropping with annuals in industrialized agricultural landscapes has advanced is with cover crops, where private, public, and governmental organizations have harmonized efforts to increase the adoption of cover crop mixtures.

Intercropping with functionally diverse crops can reduce the availability of resources that could otherwise be used by weeds. An experiment was conducted across 6 site-years in New York and Maryland in 2013 and 2014 to examine the effects of functional diversity and crop species richness on weed suppression. We compared four annual crop species that differed in stature and nitrogen acquisition traits: (1) pearl millet, (2) sorghum sudangrass, (3) cowpea, and (4) sunn hemp. Crops were seeded in monoculture and in three- and four-species mixtures using a replacement design in which monoculture seeding rates were divided by the number of species in the intercrop. Crop and weed biomass were sampled at ~45 and 90 d after planting. At the first sampling date, intercrops produced more crop biomass than monocultures in all but 1 site-year; however, weed biomass in intercrops was lower than monocultures in only 1 site-year. By the second sampling date, crop biomass was consistently greater in the intercrops than in the monocultures, and weed biomass was lower in the intercrops than in monocultures in 2 site-years. Although we observed several negative relationships between crop species richness and weed biomass, crop biomass was a more important factor than species richness for suppressing weeds. Despite the weak weed suppression from the two legumes compared with the two grasses, legume crops can provide other benefits, including increased forage quality, soil nitrogen for subsequent crops, and resources for pollinators if allowed to flower. On the other hand, if weed suppression is the top priority, our results suggest that monocultures of high biomass–producing grasses will provide more effective suppression at a lower seed cost than functionally diverse intercrops that include low biomass–producing legumes in warm-season intercrops.

A warm‐season annual intercropping experiment was conducted across the northeastern United States with four trials in 2013 and five trials in 2014 with four crop species selected based on differences in stature and N acquisition traits: (i) pearl millet [Pennisetum glaucum (L.) R. Br.], (ii) sorghum sudangrass [Sorghum bicolor (L.) Moench × S. sudanense (Piper) Stapf], (iii) cowpea [Vigna unguiculata (L.) Walp], and (iv) sunn hemp (Crotalaria juncea L.). Crops were seeded in monoculture and in three‐ and four‐species mixtures using a replacement design where monoculture seeding rates were divided by the number of species in the intercrop. Crop biomass was sampled at ∼45 and 90 d after planting. When averaged across the nine site‐years, biomass at the first and second sampling dates, respectively, of the monoculture treatments ranged from 1040 and 2500 kg ha−1 (cowpea) to 3000 and 9300 kg ha−1 (pearl millet). In general, biomass production of the legume monocultures was lower than the grass monocultures and intercrops at both sampling dates. All intercrops had land equivalent ratios (LERs) greater than one, indicating complementarity, likely a result of resource partitioning. Intercrops, particularly the four‐species mixture, exhibited greater stability in yields across environments. The pearl millet–sorghum sudangrass–sunn hemp intercrop had the greatest evenness, suggesting that species selected for annual intercrops should have similar monoculture growth rates to minimize asymmetric competition.

Cover crop mixtures have the potential to provide more ecosystem services than cover crop monocultures. However, seeding rates that are typically recommended (i.e. seeding rate of monoculture divided by the number of species in the mixture) are non‐optimized and often result in the competitive species dominating the mixture, and therefore limiting the amount of ecosystem services that are provided. We created an analytical framework for selecting seeding rates for cover crop mixtures that maximize multifunctionality while minimizing seed costs. The framework was developed using data from a field experiment, which included six response surface designs of two‐species mixtures, as well as a factorial replacement design of three‐species and four‐species mixtures. We quantified intraspecific and interspecific competition among two grasses and two legume cover crop species with grass and legume representing two functional groups: pearl millet [Pennisetum glaucum (L.) R.Br.], sorghum sudangrass [Sorghum bicolor (L.) Moench × Sorghum sudanense (Piper) Stapf], sunn hemp (Crotalaria juncea L.), and cowpea [Vigna unguiculata (L.) Walp]. Yield–density models were fit to estimate intraspecific and interspecific competition coefficients for each species in biculture. The hierarchy from most to least competitive was sorghum sudangrass > sunn hemp > pearl millet > cowpea. Intraspecific competition of a less competitive species was the greatest when the biculture was composed of two species in the same functional group. Competition coefficients were used to build models that estimated the biomass of each cover crop species in three‐species and four‐species mixtures. The competition coefficients and models were validated with an additional nine site‐years testing the same cover crop mixtures. The biomass of a species in a site‐year was accurately predicted 69% of the time (low root mean square error, correlation > 0.5, not biased, r2 > 0.5). Applying the framework, we designed three‐species and four‐species mixtures by identifying relative seeding rates that produced high biomass with high species evenness (i.e. high multifunctionality) at low seed costs based on a Pareto front analysis of 10,418 mixtures. Accounting for competition when constructing cover crop mixtures can improve the ecosystem services provided, and such an advancement is likely to lead to greater farmer adoption.

Agriculture now faces grand challenges, with crucial implications for the global future. These include the need to increase production of nutrient‐dense food, to improve agriculture's effects on soil, water, wildlife, and climate, and to enhance equity and justice in food and agricultural systems. We argue that certain politics of constructive collective action—and integral involvement of agricultural scientists in these politics—are essential for meeting grand challenges and other complex problems facing agriculture in the 21st century. To spur reflection and deliberation about the role of politics in the work of agricultural scientists, we outline these politics of constructive collective action. These serve to organize forceful responses to grand challenges through coordinated and cooperative action taken by multiple sectors of society. In essence, these politics entail (1) building bonds of affinity within a heterogenous network, (2) developing a shared roadmap for collective action, and (3) taking sustained action together. These emerging politics differ markedly from more commonly discussed forms of political activity by scientists, e.g., policy advisory, policy advocacy, and protest. We present key premises for our thesis, and then describe and discuss a politics of constructive collective action, the necessary roles of agricultural scientists, and an agenda for exploring and expanding their engagement in these politics.

Crop diversity may mediate the intensity of weed-crop competition by altering soil nutrient availability and plant-soil microbe interactions. A greenhouse experiment was conducted to analyze weed-crop competition in soils with varying crop diversity legacies. Soil greenhouse treatments included field soils (i.e., soil nutrient and microbial legacies), a sterile greenhouse potting mix inoculated with microorganisms of the field soils (i.e., microbial legacies), and a sterile greenhouse potting mix. Soils for the greenhouse experiment were sampled and assessed after two-years of conditioning with annual and perennial cropping systems under four levels of intercrop diversity. The greenhouse experiment involved growing one sorghum sudangrass (Sorghum bicolor (L.) Moench × S. sudanese Piper) crop plant and zero to six common lambsquarters (Chenopodium album L.) weed plants in soil from each diversity and cropping system treatment. The weed density treatments created a weed-crop competition gradient, which was used to quantify legacy effects of crop diversity. Weed-crop competition increased with crop diversity in both the field soil and inoculated soil treatments in the annual system. In the perennial system, differences in weed-crop competition intensity were driven by crop yield potential. In the perennial field soil treatment, crop yield potential was greatest in the highest diversity treatment, whereas in the perennial inoculated soil treatment, crop yield potential was greatest in the lowest diversity treatment. Results show potential for negative effects from previous crop diversity on weed-crop competition, and the divergent impact of microbial and nutrient legacies on crop yield potential. Future research should aim to evaluate the consistency of legacy effects and identify principles that can guide soil and crop management, especially in conservation agriculture where soil tillage and its microbial legacy reducing effects are minimized.

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Our group aims to place at the forefront the priorities of gender and sexual minorities while remaining open and welcome to all. We think it is important to first introduce some terms that are common in our community. We want to acknowledge that of these identities are fluid depending on the individual, and the definitions we list here are meant to provide scaffolding for